This invention relates to a method and apparatus for recording channels of digitized information in data tracks on a record medium and, more particularly, to such a method and apparatus wherein the digitized information is recorded in successive data blocks in at least one and, preferably, in a plurality, of data tracks, each recorded data block being separately accessible.
Digital recording techniques have been extended to various fields in which analog recording heretofore had been used. For example, high quality audio recording now can be achieved by using digital techniques. So-called PCM recorders have been proposed for recording audio signals in digital form on a suitable magnetic record medium, such as magnetic tape. U.S. Pat. Nos. 4,211,997 and 4,145,683 describe two of these digital audio recording techniques.
Typically, digital signals are recorded in various error-correction codes so as to prevent total loss of information in the event of noise, interference, dropout, and other disturbances which may obliterate a portion of the recorded data. One recent error correcting code which has been developed and which is particularly useful in recovering digitally encoded signals that may be subjected to such obliteration is the so-called cross-interleave error correction code described in, for example, U.S. application Ser. No. 218,256, filed Dec. 19, 1980. Other error-correction encoding techniques also are known, such as described in U.S. Ser. No. 195,625, filed Oct. 9, 1980. In such useful error correction codes, a number of digital words, each representing, for example, a sample of an analog signal, are grouped in data blocks. Advantageously, and as described in the aforementioned applications, such data blocks are formed of time-interleaved digital words, together with time-interleaved parity words, the latter being used, upon reproduction and time de-interleaving, to correct for errors that may be present in the digital words. The data blocks in which the aforementioned time-interleaved digital words are grouped are recorded in one or more data tracks on the record medium.
When data blocks are recorded, as aforesaid, in a PCM audio recorder, a predetermined synchronizing signal may be inserted into every recorded data block, this synchronizing signal being used, during reproduction, by a servo system to control a tape-drive capstan such that the digital signals are reproduced with proper timing relationships. Such synchronizing signals thus are reproduced with a period equal to the data block period. Typically, such reproduced synchronizing signals exhibit a relatively high repetition rate, particularly if the length, or duration, of the data block is relatively short. Such a short data block duration is advantageous in many error-correction decoding schemes. However, a relatively rapid repetition rate of this synchronizing signal which is used for carrying out a capstan servo operation places severe constraints on the tolerance of the servo system to account for jitter, timing errors due to expansion of the record medium, and the like.
PCM audio recorders offer the advantage that highly precise electronic editing may be performed. For example, in a data track, a data block, which represents a relatively small increment of audio information, may be accessed, and that data block, as well as numerous succeeding data blocks, then may be modified, replaced, or the like. The location at which this electronic editing commences is known as the "punch-in" point, and the location at which this editing terminates is known as the "punch-out" point. Of course, for optimum editing, the punch-in and punch-out points should be known with high accuracy. This can be achieved by identifying the particular data blocks which are located at the punch-in and punch-out points. Such data block identification, or access, may be obtained by providing a data block address at the beginning of each recorded data block. However, to avoid ambiguity, since a very large number of data blocks may be recorded in a data track, the data block address must be formed of a large number of bits. Consequently, the data block address may become unreasonably enlarged. For this reason, the use of a data block address at the beginning of each data block has not been enthusiastically adopted. Consequently, if a data block address is provided at the beginning of, for example, a group of ten data blocks, thereby permitting the data block address to include a smaller number of bits, the punch-in and punch-out points cannot be selected with as great a precision as would otherwise obtain if the data block address is provided in each data block.